Different techniques for industrial printing on a paper-based material are well known. For some purposes it may be suitable to separate the known techniques into two categories, namely impact printing and non-impact printing.
Examples of impact printing techniques include flexography, rotogravure, and offset printing. Common for these examples is the requirement of a master image, often called a cliché, which is at least partially covered with ink in a pattern representing the image to be printed. The cliché is then pressed against a substrate to be printed, either directly or indirectly via one or several compression cylinders, in order to transfer the ink with high resolution to the substrate. The substrate may e.g. be paper, film, laminate, or board. Impact printers are typically implemented in large scale and high speed printing systems where static images need to be printed.
On the other hand, non-impact printing techniques do not require the printer to be in direct contact with the substrate to be printed. Inkjet printers, to mention one well known technique within this category, are thus arranged at a distance from the substrate and are controlled digitally thus being capable of providing high resolution dynamic images.
Within food packaging technology impact printing techniques are so far chosen due to their high speed and robust operation in providing high quality printing of static images. Large scale printing is conventionally performed by printers being up to 2 m wide, even though a final roll fed packaging system web width only is a part of the total width such that it is possible to print up to ten parallel webs simultaneously. Roll fed substrates are generally slitted to single webs at the finalization of the substrate production for later use as a packaging material in the filling equipment.
Nevertheless impact printer, used when printing e.g. a décor layer on a carton based material for later use as a packaging material in food packaging industry, require vast amount of resources. The production of the clichés is time consuming and costly, and is dependent on the use of expensive development chemicals. Further, clichés are usually fastened by means of adhesive tape which contributes to the rather high overall cost of such system when utilized in industrial mass production applications.
Hence, it would be advantageous to replace the impact printers with non-impact printers within the food packaging material production in order to reduce time and costs of the printing process, but also for allowing a rapid change of the image to be printed without the need for a shutdown and cliché exchange. However, since there is no easy way of providing sufficiently wide non-impact printers it would be necessary to arrange several printer units adjacent to each other in order to cover the complete paper. This would also require so called stitching, which is a complex algorithm for providing a seamless continuation of the printed image where two printer units overlap. Further, it would be required to apply a significant tension to the substrate in order to ensure the correct position of each part of the substrate. However, in case of thin substrates, such as paper etc., such tensioning would increase the risk of substrate damages, as well as a reduction in the printing quality since the printed pattern will be deformed once the tension is removed from the substrate. Since the human eye is extremely sensitive for detecting misalignment of image pixels it would thus be beneficial to provide a solution utilizing overlapping non-impact printer units in an efficient and robust manner.